Assia MOUHAND - Academia.edu (original) (raw)

Papers by Assia MOUHAND

Communications Chemistry

The polyhistidine (6XHis) motif is one of the most ubiquitous protein purification tags. The 6XHi... more The polyhistidine (6XHis) motif is one of the most ubiquitous protein purification tags. The 6XHis motif enables the binding of tagged proteins to various metals, which can be advantageously used for purification with immobilized metal affinity chromatography. Despite its popularity, protein structures encompassing metal-bound 6XHis are rare. Here, we obtained a 2.5 Å resolution crystal structure of a single chain Fv antibody (scFv) bearing a C-terminal sortase motif, 6XHis and TwinStrep tags (LPETGHHHHHHWSHPQFEK[G3S]3WSHPQFEK). The structure, obtained in the presence of cobalt, reveals a unique tetramerization motif (TetrHis) stabilized by 8 Co2+ ions. The TetrHis motif contains four 6 residues-long β-strands, and each metal center coordinates 3 to 5 residues, including all 6XHis histidines. By combining dynamic light scattering, small angle x-ray scattering and molecular dynamics simulations, We investigated the influence of Co2+ on the conformational dynamics of scFv 2A2, observi...

Arrestin dependent G protein-coupled receptor (GPCR) signaling pathway is regulated by the phosph... more Arrestin dependent G protein-coupled receptor (GPCR) signaling pathway is regulated by the phosphorylation state of GPCR’s C-terminal domain, but the molecular bases of arrestin:receptor interaction are to be further illuminated. Here we investigated the impact of phosphorylation on the conformational features of the C-terminal region from three Rhodopsin-like GPCRs, the vasopressin V2 Receptor (V2R), the Growth Hormone Secretagogue or ghrelin Receptor type 1a (GHSR) and the β2-Adernergic Receptor (β2AR). Using phosphomimetic variants, we identified pre-formed secondary structure elements, or short linear motif (SLiMs), that undergo specific conformational transitions upon phosphorylation. Of importance, such conformational transition favors arrestin-2 binding. Hence, our results suggest a model in which the cellular signaling specificity of GPCRs is encoded in the phosphorylation-dependent structuration of the C-terminal regions, which will subsequently modulate arrestin conformati...

Biomolecules

Arrestin-dependent pathways are a central component of G protein-coupled receptor (GPCRs) signali... more Arrestin-dependent pathways are a central component of G protein-coupled receptor (GPCRs) signaling. However, the molecular processes regulating arrestin binding are to be further illuminated, in particular with regard to the structural impact of GPCR C-terminal disordered regions. Here, we used an integrated biophysical strategy to describe the basal conformations of the C-terminal domains of three class A GPCRs, the vasopressin V2 receptor (V2R), the growth hormone secretagogue or ghrelin receptor type 1a (GHSR) and the β2-adernergic receptor (β2AR). By doing so, we revealed the presence of transient secondary structures in these regions that are potentially involved in the interaction with arrestin. These secondary structure elements differ from those described in the literature in interaction with arrestin. This suggests a mechanism where the secondary structure conformational preferences in the C-terminal regions of GPCRs could be a central feature for optimizing arrestins reco...

Viruses, 2022

The nucleocapsid domain (NCd), located at the C-terminus of the HIV-1 Gag protein, is involved in... more The nucleocapsid domain (NCd), located at the C-terminus of the HIV-1 Gag protein, is involved in numerous stages of the replication cycle, such as the packaging of the viral genome and reverse transcription. It exists under different forms through the viral life cycle, depending on the processing of Gag by the HIV-1 protease. NCd is constituted of two adjacent zinc knuckles (ZK1 and ZK2), separated by a flexible linker and flanked by disordered regions. Here, conformational equilibria between a major and two minor states were highlighted exclusively in ZK2, by using CPMG and CEST NMR experiments. These minor states appear to be temperature dependent, and their populations are highest at physiological temperature. These minor states are present both in NCp7, the mature form of NCd, and in NCp9 and NCp15, the precursor forms of NCd, with increased populations. The role of these minor states in the targeting of NCd by drugs and its binding properties is discussed.

RNA Biology, 2022

ABSTRACT Maturation of the HIV-1 viral particles shortly after budding is required for infectivit... more ABSTRACT Maturation of the HIV-1 viral particles shortly after budding is required for infectivity. During this process, the Pr55Gag precursor undergoes a cascade of proteolytic cleavages, and whilst the structural rearrangements of the viral proteins are well understood, the concomitant maturation of the genomic RNA (gRNA) structure is unexplored, despite evidence that it is required for infectivity. To get insight into this process, we systematically analysed the interactions between Pr55Gag or its maturation products (NCp15, NCp9 and NCp7) and the 5ʹ gRNA region and their structural consequences, in vitro. We show that Pr55Gag and its maturation products mostly bind at different RNA sites and with different contributions of their two zinc knuckle domains. Importantly, these proteins have different transient and permanent effects on the RNA structure, the late NCp9 and NCp7 inducing dramatic structural rearrangements. Altogether, our results reveal the distinct contributions of the different Pr55Gag maturation products on the gRNA structural maturation.

Progress in Molecular Biology and Translational Science, 2020

G protein-coupled receptors (GPCRs) and Nuclear Receptors (NRs) are two signaling machineries tha... more G protein-coupled receptors (GPCRs) and Nuclear Receptors (NRs) are two signaling machineries that are involved in major physiological processes and, as a consequence, in a substantial number of diseases. Therefore, they actually represent two major targets for drugs with potential applications in almost all public health issues. Full exploitation of these targets for therapeutic purposes nevertheless requires opening original avenues in drug design, and this in turn implies a better understanding of the molecular mechanisms underlying their functioning. However, full comprehension of how these complex systems function and how they are deregulated in a physiopathological context is obscured by the fact that these proteins include a substantial number of disordered regions that are central to their mechanism of action but whose structural and functional properties are still largely unexplored. In this chapter, we describe how these intrinsically disordered regions (IDR) or proteins (IDP) intervene, control and finely modulate the thermodynamics of complexes involved in GPCR and NR regulation, which in turn triggers a multitude of cascade of events that are exquisitely orchestrated to ultimately control the biological output.

Nucleic Acids Research, 2018

During HIV-1 assembly and budding, Gag protein, in particular the C-terminal domain containing th... more During HIV-1 assembly and budding, Gag protein, in particular the C-terminal domain containing the nucleocapsid domain (NCd), p1 and p6, is the site of numerous interactions with viral and cellular factors. Most in vitro studies of Gag have used constructs lacking p1 and p6. Here, using NMR spectroscopy, we show that the p1-p6 region of Gag (NCp15) is largely disordered, but interacts transiently with the NCd. These interactions modify the dynamic properties of the NCd. Indeed, using isothermal titration calorimetry (ITC), we have measured a higher entropic penalty to RNA-binding for the NCd precursor, NCp15, than for the mature form, NCp7, which lacks p1 and p6. We propose that during assembly and budding of virions, concomitant with Gag oligomerization, transient interactions between NCd and p1-p6 become salient and responsible for (i) a higher level of structuration of p6, which favours recruitment of budding partners; and (ii) a higher entropic penalty to RNA-binding at specific sites that favours non-specific binding of NCd at multiple sites on the genomic RNA (gRNA). The contributions of p6 and p1 are sequentially removed via proteolysis during Gag maturation such that the RNA-binding specificity of the mature protein is governed by the properties of NCd.

Biochimica et biophysica acta, Jun 1, 2018

HIV-1 Gag polyprotein orchestrates the assembly of viral particles. Its C-terminus consists of th... more HIV-1 Gag polyprotein orchestrates the assembly of viral particles. Its C-terminus consists of the nucleocapsid (NC) domain that interacts with RNA, and the p6 domain containing the PTAP motif that binds the cellular ESCRT factor TSG101 and ALIX. Deletion of the NC domain of Gag (GagNC) results in defective Gag assembly, a decrease in virus production and, thus probably affects recruitment of the ESCRT machinery. To investigate the role of GagNC in this recruitment, we analysed its impact on TSG101 and ALIX localisations and interactions in cells expressing Gag. Cells expressing mCherry-Gag or derivatives, alone or together with eGFP-TSG101 or eGFP-ALIX, were analysed by confocal microscopy and FLIM-FRET. Chemical shift mapping between TSG101-UEV motif and Gag C-terminus was performed by NMR. We show that deletion of NC or of its two zinc fingers decreases the amount of Gag-TSG101 interacting complexes in cells. These findings are supported by NMR data showing chemical shift perturb...

Journal of Biomolecular NMR, 2005

The polyhistidine (6XHis) tag is one of the most ubiquitous fusion tags used for the purification... more The polyhistidine (6XHis) tag is one of the most ubiquitous fusion tags used for the purification of recombinant proteins. The 6XHis motif enables the tagged protein to bind metal ions such as Co2+, Ni2+, Zn2+ and Cu2+, which can be advantageously used for protein purification with immobilized metal affinity chromatography (IMAC). Despite its widespread use, high-resolution protein structures encompassing a metal-bound 6XHis motif rarely occur in the worldwide Protein Data Bank (PDB). Here, we obtained a 2.5 Å resolution crystal structure of a single chain variable fragment (scFv) antibody bearing a C-terminal tag composed of a sortase motif (LPETG), followed by a 6XHis and a TwinStrep tag (WSHPQFEK[G3S]3WSHPQFEK). The protein crystallized in the presence of cobalt (II) and its structure reveals a novel tetramerization motif (TetrHis) stabilized by 8 Co2+ ions clustered within a small region of space. The TetrHis motif contains two 6 residues-long β-strands related by a twofold symm...

Journal of molecular biology, 2020

Intrinsically Disordered Proteins (IDPs) play key functional roles facilitated by their inherent ... more Intrinsically Disordered Proteins (IDPs) play key functional roles facilitated by their inherent plasticity. In most of the cases, IDPs recognize their partners through partially-structured elements inserted in fully-disordered chains. The identification and characterization of these elements is fundamental to understand the functional mechanisms of IDPs. Although several computational methods have been developed to identify order within disordered chains, most of the current secondary structure predictors are focused on globular proteins and are not necessarily appropriate for IDPs. Here, we present a comprehensible method, called Local Structural Propensity Predictor (LS2P), to predict secondary structure elements from IDP sequences. LS2P performs statistical analyses from a database of three-residue fragments extracted from coil regions of high-resolution protein structures. In addition to identifying scarcely populated helical and extended regions, the method pinpoints short str...

Viruses